Aircraft icing is a serious threat to aviation safety. Icing accretion process usually interacts with surface water run back flow under glaze icing condition. Advancing the technology for safe and efficient aircraft operation in icing conditions requires a better understanding of the underlying physics of complicated thermal flow phenomena pertinent to aircraft icing phenomena, both for the icing itself as well as for the water runback along contaminated surfaces of wing surface. In the present study, an experimental investigation was conducted to characterize the surface wind-driven water film/rivulet flows over a NACA 0012 airfoil in order to elucidate the underlying physics of the transient surface water transport behavior pertinent to aircraft icing phenomena. The experimental study was conducted in an icing research wind tunnel available at Aerospace Engineering Department of Iowa State University, was developed and applied to achieve Quantitative measurements of the unsteady film/rivulet flows were achieved by a novel digital image projection (DIP) measurement system. The measurement results reveal clearly that, after impinged on the leading edge of the NACA0012 airfoil, the micro-sized water droplets would coalesce to form a thin water film in the region near the leading edge of the airfoil. The formation of rivulets was found to be a time-dependent process, which relies on the initial water runback flow structure. The time-averaged leading edge film thickness follows the Nelson's x~(1/4) scaling law for all of the free stream velocities.
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